The present invention relates to a turbocharger impeller, a method of manufacturing the same, a turbocharger, and a turbocharger unit.
A turbocharger is used, for example, for an internal combustion engine mounted in a vehicle. The turbocharger recovers energy of an exhaust gas of the internal combustion engine through a turbine. The recovered energy rotates an impeller (compressor) connected to the turbine via a shaft. The impeller rotates, and the internal combustion engine is supercharged with intake air. As a result, the intake efficiency is enhanced, and the internal combustion engine is improved in terms of output and of fuel efficiency.
The turbine, or impeller, may include a substantially truncated cone-shaped hub portion, and a plurality of vane portions, formed on a surface of the hub portion, that extend outward from a periphery thereof. The vane portions force-feed a fluid (i.e. intake air) in the radially outward direction relative to the surface of the hub portion. Further, the vane portions, described above, may be precisely positioned and/or configured within the turbocharger as a whole to achieve a desired improvement in engine intake efficiency. Accordingly, the impeller may be produced via precision investment casting. However, precision investment casting often requires a relatively long operation and/or production cycle time to complete, relative to other forms of casting, for example. Thus, a method to manufacture impellers with a short operation time is desired.
However, instead of producing the impeller via precision investment casting, alternative methods, such as machining a base material such as an extruded material, may be employed. Machining, however, may create various undesirable grooves due to the machining on the surfaces of the vane portions and/or the hub portion. Such a groove may create and/or increase turbulence experienced by a fluid flowing across an impeller. As a result, an impeller made by machining may actually diminish engine intake efficiency due to turbulence caused by grooves and/or other imperfections in the impeller, in comparison an impeller formed by precision investment casting.
To address the issues presented above, post-production surface processing of the vane portions and the hub portion may be performed to eliminate the grooves. However, such surface processing may require an even longer period of time to complete, compared with the conventional precision investment casting, thus the method may not desirable for efficient high-volume impeller production. Currently, there may be a need for an impeller able to maintain pressure loss within a desirable, i.e. an optimal range, such as that associated with an impeller produced by precision investment casting while leaving grooves. Because of leaving the grooves, the impeller can be machined from the base material in a shorter time. By providing a construction helping to suppress pressure loss, it is possible to realize an intake efficiency equivalent to that of the impeller produced by precision investment casting.
Japanese Laid-Open Patent Publication No. 2005-163640 (referred to as publication 640) generally discloses an impeller of a compressor. The impeller includes a hub portion and vane portions that extend outwardly thereof. Grooves extend linearly across wing surfaces of the vane portions. The groove prevent enlargement of a boundary layer (a boundary layer of a fluid flow) generated on a surface of the hub portion or separation of the flow. As a result, the efficiency of the compressor is enhanced.
Japanese Laid-Open Patent Publication No. H09-100797 (referred to as publication 797) discloses a vane wheel (i.e. corresponding to an impeller) of a centrifugal compressor. The vane wheel includes a hub portion and vane portions that extend outwardly thereof. In the vane portions, grooves are formed to extend from fluid inlet portions to intermediate positions. Each groove may be formed with a predetermined groove width, interval, and depth to conform to a fluid flowing direction as directed by the vane portions during rotation of the vane wheel.
Japanese Laid-Open Patent Publication No. 2003-120574 (referred to as publication 574) discloses a vane wheel (i.e. corresponding to an impeller) of a motor pump. The vane wheel includes a hub portion and vane portions that extend outwardly thereof. Grooves are formed to extend in a rotational direction on a surface of the vane portions. In detail, the grooves may be formed such that an outer peripheral region and an inner peripheral region of the vane wheel accommodate equivalent fluid feeding amounts. In the inner peripheral region, the space between separating each of the grooves is set to be large. In the outer peripheral region, the space between separating each of the grooves is set to be small.
When machining an impeller from a base material, a groove remains on the surface of the impeller portion due to the machining. The groove may direct and/or guide fluid flow. Such grooves are need for allowing the impeller to suppress pressure loss to achieve intake efficiency equivalent to that of an impeller formed by precision investment casting. In comparison, the above-discussed publication 640, publication 797, and publication 574 may not disclose a method of machining the impeller from a base material.
Publication 640 discloses grooves formed in the hub portion. Publication 797 discloses grooves formed in the vane portions. However, both sets of grooves, in publication 640 and publication 797, are formed in order to prevent enlargement of a boundary layer of a fluid at a central portion of the impeller and/or undesirable separation of fluid flow. Thus, these grooves may not be formed to suppress pressure loss at an inlet portion.
Moreover, the grooves described in publication 640, publication 797, and publication 574 are formed in a process subsequent to impeller fabrication. For example, after manufacturing the impeller by conventional production methods, grooves are then formed in the impeller by a separate process. Thus, these methods do not help to produce the impeller in a shorter time.
Specifically, as disclosed by publication 640, the hub portion includes a groove, whereas there no grooves are present in the vane portions. In a technique disclosed by publication 797, the vane portions include grooves. The grooves disclosed by publication 797, however, are formed at equal intervals and with a predetermined depth in the impeller. Such grooves are formed only at the fluid inlet portions of the vane portions and extend to regions that correspond to intermediate positions of the vane portions. As discussed in publication 574, grooves are formed in the vane portions. The space between separating each of the grooves is smaller in the outer peripheral region than in the inner peripheral region. As a result, similar and/or identical amounts of fluid may be easily and/or uniformly dispersed about the outer peripheral region at the rear of the vane portions as the inner peripheral region of the vane portions. The grooves, however, are of equal depth.
There is a need in the art for an impeller of a turbocharger that provides highintake efficiency and may be manufactured by an efficient and/or relatively inexpensive process.